Lambda the Ultimate

Extensible Records With Scoped Labels
Daan Leijen

Records provide a safe and flexible way to construct data structures. We describe a natural approach to typing polymorphic and extensible records that is simple, easy to use in practice, and straightforward to implement. A novel aspect of this work is that records can contain duplicate labels, effectively introducing a form of scoping over the labels. Furthermore, it is a fully orthogonal extension to existing type systems and programming languages...

Last time one of Daan's papers was mentioned, there was a very positive response (after Frank reminded us a couple of times). This is equally good: clever, elegant, and clearly presented.

(Between this and the Sheard paper, it's a good week for practical type systems...)